In manufacturing an aircraft, for example, many holes are formed manually in a constructional member made of high hardness aluminum alloy used for aircrafts or in overlapped plates having a great thickness. In such a process, a two-edge stepped double margin drill is used as a drill. The two-edge double margin drill has a configuration as described in Japanese Unexamined Patent Application Publication No. 2006-205272 and has two margins. According to such a configuration, an inner peripheral surface of an obtained hole has high smoothness and holes are processed with high accuracy. Such a two-edge stepped double margin drill includes a drill having a small diameter at a distal end thereof. In processing a material for aircrafts, occurrence of cutting distortion is strictly required to be eliminated. The cutting margin generated via one performance of a process of drilling a hole is necessarily set small so that a diameter of the hole can be gradually increased. The cutting margin corresponds to difference between an outer peripheral dimension of a distal end side small diameter portion of the stepped drill and an outer peripheral dimension of a basal end side large diameter portion.